My understanding is that the Glass Steagall act in the 1930s was passed to separate holding banks (like WaMu etc) and investment banks (GS) because when they were combined certain risks popped up.
One of the first that immediately comes to mind is that now investment banks will be in charge of deposits. Securities trading is pretty risky (especially when you're leveraged) and if something should happen (tech bubble or the current mess) then the deposits are threatened. Since deposits are also insured by the government (FDIC), the government then is automatically on the hook for the money.
This means that there is a need for new restrictions placed on the hybrid banks. If the regulation is too low, then we run the risk of putting deposits in danger. If the regulation is too much, we run the risk of crippling the investment banking industry.
Then again other countries seem to work fine without such separation, so hopefully this will work out. From the article it seems new regulations will be imposed on the banks.
If anyone else has additional insight, feel free to correct me :)